sem_post(3) - NetBSD Manual Pages

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SEM_POST(3)             NetBSD Library Functions Manual            SEM_POST(3)


NAME

     sem_post -- increment (unlock) a semaphore


LIBRARY

     POSIX Real-time Library (librt, -lrt)


SYNOPSIS

     #include <semaphore.h>

     int
     sem_post(sem_t *sem);


DESCRIPTION

     The sem_post() function increments (unlocks) the semaphore pointed to by
     sem.  If there are threads blocked on the semaphore when sem_post() is
     called, then the highest priority thread that has been blocked the long-
     est on the semaphore will be allowed to return from sem_wait() or
     sem_timedwait().

     sem_post() is signal-reentrant and may be called within signal handlers.


RETURN VALUES

     The sem_post() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.


ERRORS

     sem_post() will fail if:

     [EINVAL]           sem points to an invalid semaphore.


SEE ALSO

     sem_timedwait(3), sem_trywait(3), sem_wait(3)


STANDARDS

     sem_post() conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').

NetBSD 8.2                     February 29, 2012                    NetBSD 8.2